Piston with central cooling gallery cooling feature

ABSTRACT

A piston includes an upper crown portion and a lower crown portion with a pair of pin bosses spaced for receipt of a connecting rod. The pin bosses have pin bores aligned with one another along a pin bore axis. The upper crown portion and the lower crown portion form an outer oil gallery and a central oil gallery. The central oil gallery is formed in part by a floor extending radially inwardly from the outer oil gallery to a plateau. To facilitate cooling the central gallery, the plateau has a through opening and the floor has at least one trough depending axially therein. At least one oil flow passage extends in fluid communication between the outer oil gallery and the central oil gallery, wherein at least one oil flow passage is axially aligned with the at least one trough to provide a direct flow of oil to the trough.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 61/301,039, filed Feb. 3, 2010, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to pistons for internal combustionengines, and more particularly to pistons having a central oil coolinggallery.

2. Related Art

Piston constructions having a central oil cooling gallery or twosubstantially closed oil cooling galleries (dual galleries) are known.The dual gallery pistons have an annular, radially outer gallery and anopen central gallery formed between upper and lower crown portions. Theouter and central galleries can be isolated from one another or in fluidcommunication with one another via oil passages. In addition, it isknown to provide pin lubrication passages extending from one or both ofthe galleries to a wrist pin. The lubrication passages can extend into awrist pin bore of a pin boss and/or between laterally spaced pin bosses.The outer gallery is particularly suited for cooling a ring belt regionof the piston, while the central gallery is particularly suited forcooling a central crown region formed in part by a combustion bowl wall,which is exposed to hot combustion gasses.

The combustion bowl and central crown region is exposed to extreme heatin use. As such, the aforementioned central gallery needs to receiveample oil flow in order to provide adequately cooling to the centralgallery region. Although central galleries, both closed and open, areknown, issues remain in providing adequate cooling in the central crownregion. In particular, continual efforts remain to both providesufficient oil flow through the central crown region while at the sametime avoiding “cooking” and deteriorating the oil. If the oil directedto the central gallery region is allowed to remain in the region for toolong without being recirculated, the oil “cooks”, thereby diminishingboth the cooling and lubrication capacity of the oil. On the other hand,if the oil is allowed to flow outwardly from the central gallery tooquickly, the cooling function of the oil is diminished, therebypotentially reducing the useful life of the piston.

SUMMARY OF THE INVENTION

A piston includes a piston body having an upper crown portion with anupper combustion wall against which combustion forces act and a lowercrown portion with a pair of pin bosses spaced for receipt of a smallend of a connecting rod in a pin bore region therebetween. The pinbosses have pin bores aligned with one another along a pin bore axisthat extends transversely to a longitudinal central axis along which thepiston translates. The upper crown portion and the lower crown portionform an outer oil gallery and a central oil gallery. The central oilgallery is formed in part by a floor extending radially inwardly fromthe outer oil gallery to a plateau. To further facilitate cooling thecentral gallery, the plateau has a through opening and the floor has atleast one trough depending axially therein. At least one oil flowpassage extends in fluid communication between the outer oil gallery andthe central oil gallery, wherein at least one oil flow passage isaxially aligned with the at least one trough.

In accordance with another aspect of the invention, the piston has apair of troughs diametrically opposite one another.

In accordance with yet another aspect of the invention, the troughs arediametrically aligned along the pin bore axis.

In accordance with yet another aspect of the invention, each troughextends between about 45 to 90 degrees about the central gallery.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of the invention willbecome more readily appreciated when considered in connection with thefollowing detailed description of presently preferred embodiments andbest mode, appended claims and accompanying drawings, in which:

FIG. 1 is a cross-sectional view taken generally along a pin bore axisof a piston constructed in accordance with one presently preferredaspect of the invention;

FIG. 2 is a cross-sectional view of the piston of FIG. 1 taken generallyalong an axis extending transversely to the pin bore axis;

FIG. 3 is a broken-away perspective view of the piston of FIG. 1;

FIG. 4 is a plan view of a lower crown of the piston of FIG. 1 lookinggenerally along the line 4-4 of FIG. 1;

FIG. 5 is a plan view looking down on the lower crown of the piston ofFIG. 1; and

FIG. 6 is a perspective view of the lower crown of the piston of FIG. 1.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

Referring in more detail to the drawings, FIGS. 1-3 illustrate a piston10 constructed in accordance with one presently preferred aspect of theinvention. The piston 10 has a piston body 12 extending along alongitudinal central axis 14 along which the piston body 12 reciprocateswithin a cylinder bore (not shown). The piston body 12 includes an uppercrown portion 16 having an upper combustion wall 18, represented here,by way of example and without limitation, as providing a recessedcombustion bowl 20, against which combustion forces directly act in thecylinder bore, thereby providing a location where extreme heat isgenerated. As referenced in FIG. 1, for sake of simplicity, the uppercrown portion 16 has at least one, and shown here as a pair of annularupper ribs, referred to hereafter as an upper inner rib 22 and upperouter rib 24, depending from the upper combustion wall 18 to respectivefree ends 26, 28. The piston body 12 further includes a lower crownportion 30 having at least one, and shown here as a pair of annularlower ribs, referred to hereafter as a lower inner rib 32 and lowerouter rib 34, extending to respective free ends 36, 38 configured forabutment with the free ends 26, 28 of the upper ribs to provide, atleast in part, an inner or central oil gallery 37 and an annular outeroil gallery 39 extending about the central oil gallery 37. The lowercrown portion 30 further includes an inner gallery lower wall, alsoreferred to as floor 40, extending radially inwardly in ascendingrelation from the lower inner rib 32 to a generally planar, raisedplateau 41 to partially enclose the central oil gallery 37. A pair ofpin bosses 42, 44 depend generally from the floor 40 to provide a pairof wrist pin bores 43, 45 aligned along a pin bore axis 47 for receiptof a wrist pin (not shown) with a space 46 provided between the pinbosses 42, 44 for receipt of a small end of a connecting rod (notshown). The floor 40 provides a central gallery cooling feature tofacilitate cooling the upper combustion wall 18, including at least onetrough, and shown here as a pair of troughs 48 depending axially thereinin axial alignment with the pin bore axis 47, such that theconfiguration of the floor 40 is circumferentially non-uniform. Thetroughs 48 each extend between about 45 to 90 degrees about the centralgallery. Further, the plateau 41 has a through opening 50 extendingtherethrough generally coaxial with the axis 14 to bring the central oilgallery 37 into direct fluid communication with the space 46 in the pinbore region. As such, the configuration of the floor 40, particularlyincluding the troughs 48 and the through opening 50, plays aninstrumental role in regulating the flow of oil within and out of thecentral oil gallery 37 to provide an optimal oil flow such that optimalcooling results without “cooking” the oil. Further, the lower crownportion 30 has a pair of skirt portions 49 spaced diametrically oppositeone another on opposite sides of the pin bore axis 47.

The upper crown portion 16 is formed having an annular outer oil gallerypocket 51 extending from the inner and outer rib free ends 26, 28upwardly into an upper ring belt region 52 and an annular inner oilgallery pocket 54 extending from the inner free end 26 and upwardlybeneath the combustion bowl 20. The lower crown portion 30 is formed,such as in a casting or forging process from steel or other metal,having an annular outer oil gallery pocket 56 extending from the innerand outer rib free ends 36, 38 downwardly into a lower ring belt region58 and an annular inner oil gallery pocket 60 extending from the innerfree end 36 downwardly to the valley or trough 48 of the floor 40. Uponattaching the upper crown portion 16 to the lower crown portion 30, theannular outer oil gallery 39, represented here as being substantiallyclosed, and the inner or central oil gallery 37 is formed. The outer oilgallery 39 is bounded by the outer ribs 24, 34 and inner ribs 22, 32,while the central oil gallery 37 is bounded by the inner ribs 22, 32,the upper combustion wall 18 and the floor 40.

To facilitate cooling the piston 10, one or more oil flow passages areprovided in the lower rib 32. For example, as shown in FIG. 1, a pair ofoil flow passages 62 extend diametrically opposite one another throughthe lower inner rib 32 generally along and axially aligned with the pinbore axis 47, and as shown in FIG. 2, another pair of diametricallyopposite oil flow passages 64, which are spaced radially from the oilflow passages 62, extend through the lower inner rib 32, shown asextending generally transversely to the pin bore axis 47 to bring theouter oil gallery 39 into fluid communication with the inner or centraloil gallery 37. It should be recognized that the oil flow passages 64can be formed in any radial/angular configuration to channel oil fromthe outer oil gallery 39 to the central oil gallery 37, and that theyneed not extend transversely to the oil passages 62. The oil flowpassages 62 ascend from a lower most portion of the outer oil gallery 39to a location spaced axially above the troughs 48 of the floor 40 tochannel oil efficiently and directly into the troughs 38, and the oilflow passages 64 ascend from a lower most portion of the outer oilgallery 39 to a lowermost portion of the floor 40. Accordingly, thetroughs 48, being fed directly with oil from the oil passages 62,provide a temporary pooling area for the oil so that it can bemaintained for a limited period of time within the central oil gallery37 to maximized its cooling capacity prior to being channeled outwardlyfrom the central oil gallery 37 via the through opening 50.

Further, as shown in FIGS. 4 and 5, a pair of respective inlet andoutlet oil flow openings 66, 68 extend through the lower most floor ofthe outer oil gallery pocket 56 in diametrically opposed relation to oneanother generally 45 degrees from the axis 47. As such, oil from thecrankcase is able to flow upwardly into the outer oil gallery 39 throughthe inlet opening 66, whereupon the oil is circulated about the outeroil gallery 39 and channeled inwardly through the oil flow passages 62,64 into the substantially closed central oil gallery 37. Further, oilcan flow downwardly out of the outer oil gallery 39 through the outletopening 68.

Upon the oil being channeled into the central oil gallery 37, apredetermined quantity of the oil is maintained within the central oilgallery 37 and shaken in “cocktail” shaker type fashion before it ischanneled outwardly from the central oil gallery 37 via the throughpassage 50. To facilitate channeling the oil within the central oilgallery 37, a quantity of the oil flows within the closed bottom troughs48, and thus, this oil is maintained within the central oil gallery 37and kept from exiting the central oil gallery 37 prior to its expendingits full useful cooling capacity. Of course, the oil is continuouslyflowing within the central oil gallery 37, and so, the oil flowingthrough the troughs 48 is continuously recycled. Upon expending its fulluseful cooling capacity, the oil is channeled outwardly from the centraloil gallery 37 via the through opening 50.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of any ultimately allowed claimsstemming herefrom, the invention may be practiced otherwise than asspecifically described.

1. A piston, comprising: a piston body extending along a central axisalong which the piston reciprocates and having an upper crown portionwith an upper combustion wall against which combustion forces act and alower crown portion with a pair of pin bosses spaced for receipt of asmall end of a connecting rod therebetween, said pin bosses having pinbores aligned with one another along a pin bore axis, said upper crownportion and said lower crown portion forming an outer oil gallery and acentral oil gallery; said central oil gallery being formed in part by afloor extending radially inwardly from said outer oil gallery to aplateau, said plateau having a through opening and said floor having atleast one trough depending axially therein; at least one oil flowpassage extending in fluid communication between said outer oil galleryand said central oil gallery; and wherein at least one of said at leastone oil flow passage is axially aligned with said at least one trough.2. The piston of claim 1 wherein said at least one trough includes apair of diametrically opposite troughs.
 3. The piston of claim 2 whereineach one of said pair of troughs has a separate one of said at least oneoil flow passage axially aligned therewith.
 4. The piston of claim 3wherein said pair of troughs are axially aligned with said pin boreaxis.
 5. The piston of claim 1 wherein said at least one of said atleast one oil flow passage is axially spaced from said at least onetrough.
 6. The piston of claim 1 wherein said at least one oil flowpassage includes at least one oil flow passage spaced radially from saidat least one trough.
 7. The piston of claim 1 wherein said at least onetrough is axially aligned with said pin bore axis.
 8. The piston ofclaim 7 wherein said at least one of said at least one oil flow passageis axially aligned with said pin bore axis.
 9. The piston of claim 1wherein said at least one trough extends between about 45 to 90 degreesabout the central gallery.